The present invention relates to a fuel injection system particularly of an outboard motor of an electrically controlled fuel injection type.
An outboard motor is generally equipped with a two-cycle engine in which fuel is supplied in accordance with an electrically controlled fuel injection (EFI) system.
In the EFI system, a fuel injector is located in an air intake passage connected to a crank chamber of an engine and the air supply quantity is controlled by a throttle valve and fuel injection quantity is controlled by an electrical control apparatus which calculates the most suitable air supply quantity in response to load in the crank chamber and the air intake passage. The fuel pumped up by a high pressure pump from a fuel tank is always supplied to the fuel injector and the fuel not consumed in the fuel injector is returned to the fuel tank.
In the outboard motor of the type described above and including the fuel tank equipped on the side of a hull body, it is necessary to arrange a long pipe or conduit. In order to obviates this inconvenience, a vapor separator as a sub-tank is equipped in the outboard motor body and the fuel supply to the fuel injector and the fuel return are performed mainly by means of the vapor separator. In the vapor separator, a float valve is disposed to thereby maintain a constant quantity of the fuel under the fuel supply from a main fuel tank disposed in the hull body.
However, in the vapor separator disposed in the outboard motor body, vapors generated therein are floated near the engine unit including electrical elements or parts, so that some countermeasure against explosion due to the vapors will be needed.
In order to prevent such adverse phenomenon, U.S. Pat. No. 4794889 discloses a technology in which an air vent for bleeding the vapor in the vapor separator is connected to the downstream side of a throttle valve in an air intake passage to thereby bleed the vapor into a crank case.
Even in this technology, however, there is a fear of sucking the fuel in addition to the vapor into the crank case in a case when the absolute boost pressure in the air intake passage is high (for example, when the degree of opening of the throttle valve is small at the high rotation speed due to rapid deceleration), resulting in engine trouble.
Moreover, in the system described above, in which the load in the air intake passage is detected for the purpose of calculating the fuel injection quantity, the load is unevenly detected because of the inclusion of the vapor and the degree of the inclusion is not measured specifically, so that the fuel quantity is erroneously measured, thus degrading the performance of the engine.
Furthermore, the vapor separator usually comprises a tank body having a flat bottom to which a fuel supply pipe is connected and an upper portion to which a fuel return pipe is connected. In this arrangement, however, a connecting port for the return pipe is formed on the upper portion of the vapor separator. Accordingly, the return fuel passing the return pipe is directly dropped on the fuel stored in the tank body from the upper portion of the fuel in liquid state. Thus, air bubbles may be continuously caused in the fuel stored in the tank body bY the impact of the dropped fuel through the connecting port for the return pipe. These air bubbles may be liable to be sucked into a fuel supply pipe together with the fuel. In such an adverse case, the fuel including the air bubbles may be fed into the fuel injector, thus not ensuring suitable fuel injection.
In another adverse case, in which the port connected to the fuel supply pipe may be exposed to the atmosphere when the liquid surface of the fuel in the tank body of the vapor separator is largely inclined due to the centrifugal force at a time when the hull is rapidly and largely turned, atmospheric air may also be introduced into the fuel supply pipe. In such a case, the fuel including the air may be fed into the fuel injector, thus also not ensuring suitable fuel injection.